Project Summary Optogenetic approaches, which include the activation, inhibition and modulation of specific circuit components using light-sensitive genetically-encodable proteins, have greatly advanced our ability to study how the brain gives rise to behavior. The ability to manipulate and observe the activity of specific cell-types with millisecond precision has completely revolutionized the field of neuroscience and launched us into an era of studying neural circuits, including those deep within the brain such as the basal ganglia or limbic circuits. Indeed some of the most impactful studies in a number of fields have been made possible with optogenetics, including breakthroughs made in understanding sleep processes, emotional valence processing, memory formation, habit formation, reward seeking and compulsive drug-taking behaviors. The 2018 ?Optogenetic approaches to understanding neural circuits and behavior? which will be held July 15 ? 20, 2018 at the Sunday River Resort, Newry, ME will be second meeting ? following up on a very successful inaugural meeting. The development of this meeting has been hotly anticipated as similar one-time meetings have been wildly successful in terms of the participants, the lively discussion, and the impact on future work. Now, we have turned to the Gordon Research Conference (GRC) format to establish a meeting that will occur with regularity (biennially) and will feature the most exciting unpublished findings from internationally renowned basic and clinical researchers. The long-term goals of this meeting are to bring all fields of neural circuit investigation up to the same high standard and to advance our understanding of neural circuits in the context of disease-relevant behaviors. By understanding the neural circuit mechanisms of various disease states, we will have a much stronger foundation from which we can launch new biomarkers for individualized medicine and to develop circuit- informed therapies that will be more specific with fewer undesirable side-effects.